Basic air lift pumps and diffusers for the introduction of either coarse, medium or fine gas bubbles into a body of water have been known for a great many years. In actual fact, air lift pumps have been available for almost two centuries, and gas diffusers of one type or another have been known for at least as long. These two well known devices have likewise been combined for many years to form air lift diffusers for use in the aeration of a body of water, but none of these combinations have been as effective as was expected.
Various efforts have been made, for example, to increase the pumping capacity of the rising column of water and entrained air bubbles in the air lift tube, by the introduction of impellers or other devices located in the air lift tube. Improvements have also been available for at least the past 10 years that are designed to break up coarse bubbles in the air lift tube to gain high transfer efficiencies.
However, the benefits of providing unobstructed paths (neither too small nor too large) both for the water entering at the bottom of the air lift diffuser from the body of water being aerated, and for the rising column of water and air bubbles below and within that tube have prior to the present invention not been recognized.
Nor, apparently because it was desired to take advantage of the more rapidly rising coarse bubbles, have the benefits of employing fine gas bubbles in an air lift diffuser been recognized, even though various types of diffusers that emit fine gas bubbles have been known for several decades. These known air lift diffusers that utilize coarse gas bubbles require a larger volume of gas flow to lift a given volume of water, and produce a lower volume of absorption of oxygen into the pumped water, than is the case with the present invention.